It's best that that's on a pro-cannabis site. You can't deny that there are some possible bad effects from smoking marijuana. That would be lying, which is exactly what the government has been doing to us for all of these years. The best things is to put the real facts forward. Marijuana isn't perfectly harmless, but shit, if anyone can give me an example of something that's perfectly harmless they should be up for a Nobel Prize.
Kleenexes are completely harmless.